Make get_session() readonly and throw an exception if session cannot be found rather...

Make get_session() readonly and throw an exception if session cannot be found rather than trying to create it, make get_account() throw an exception if not signed in, make get_navigation() and the related navbar logic throw useful exceptions if the navigation tree doesn't exist or doesn't the match site pages, make get_nodemailer throw useful exceptions if the nodemailer data doesn't exist